Solar Lattice

FailureMode

Backsheet bubbling and deformation

ID
fm:backsheet-deformation
IRI
https://solarlattice.org/kb/fm/backsheet-deformation
Status
active
Also known as
Backsheet delamination, internal delamination, Blisters

Backsheet bubbling and deformation happens when the polymer backsheet separates from the encapsulant, or when its layers separate from each other, leaving an air gap. From the rear the backsheet looks wavy, with local bumps, bubbles or ripples, and in bad cases one or more layers peel off. Common drivers are thermo-mechanical stress, incompatible materials, heat, UV and moisture, external mechanical stress, and poor lamination; hot spots can also cause gas bubbles. Confirm it by visual inspection of the rear side, with insulation testing when safety is in doubt. A bubble in the open centre of the back is a minor issue, but delamination at the module edge or near the junction box is a serious safety risk because of water ingress, ground faults and possible arcing. Replace modules that pose a direct safety risk or that fail insulation or wet-leakage tests, and keep inspecting the remaining ones. Ground fault detection should always be active, and certification and bill of materials should be checked to prevent this failure.

<!-- review notes

Claims

affects

c1 drafted · lead Backsheet

c2 drafted · lead Encapsulant

Backsheet can separate from the encapsulant, sometimes exposing it.

presents_as

c3 verified · fact Backsheet bubbles or ripples

Backsheet looks wavy with local bumps, bubbles or ripples; in the worst case layers peel off.

verified by: joshuahamsaverified on: 2026-10-20

caused_by

c4 drafted · lead Thermal cycling

Thermo-mechanical stress from differing thermal expansion of the polymer layers.

c5 drafted · lead Material incompatibility

Chemical reactions at interfaces or additive migration between encapsulant and backsheet films.

c6 drafted · lead High operating temperature

Heat attack degrades interfacial bonding.

c7 verified · fact UV exposure

verified by: joshuahamsaverified on: 2026-10-20

c8 drafted · lead Moisture exposure

c9 drafted · lead Humid climate

More frequent and severe in hot and humid conditions.

c10 drafted · lead Mechanical stress

External mechanical stress applied to the module.

c11 drafted · lead Manufacturing defect

Insufficient lamination process, such as too short lamination times.

Delamination can be also caused by an insufficient lamination process e.g. too short lamination times.

c12 drafted · lead Module Hotspot from Cell Damage

Local overheating from hot cells or hot spots can cause gas formation in encapsulant and backsheet, and bubbles that may burst.

review note: support check: partial - Hot spots causing gas formation and bursted bubbles are stated, but in backsheet cracking context, not explicitly as cause of bubbling/deformation (delamination).

detected_by

c13 drafted · lead Visual inspection

c14 drafted · lead Insulation resistance testing

Listed as a secondary detection method (INS).

c15 drafted · lead Wet leakage current test

Modules failing insulation or wet-leakage tests should be replaced.

review note: support check: partial - Wet-leakage test appears only in the corrective action for failing modules, not as a listed detection method for this defect.

leads_to

c16 drafted · lead Loss of electrical insulation

Edge delamination can let rain or dew water in and create an electrical path to ground.

c17 drafted · lead Junction Box Failure

Delamination near the junction box can loosen it and stress live components.

review note: support check: partial - Delamination near the junction box can loosen it and stress live components with breakage danger, but 'junction box failure' is only implied.

c18 drafted · lead Arc fault

A break from a loosened junction box can disconnect a bypass diode and may cause an unmitigated arc.

distinguished_from

c19 drafted · lead Backsheet Chalking — told apart by Tactile inspection

Chalking leaves a removable white powder felt by passing a finger over a dull surface; deformation shows as bubbles, ripples or peeling layers.

review note: support check: partial - Chalking is described as removable powder felt by finger and deformation as bubbles/ripples, but no passage presents tactile inspection as a way to distinguish them.

mitigated_by

c20 drafted · lead Module replacement

Replace modules with a direct safety risk or highest severity.

c21 drafted · lead Close monitoring

Regular inspections of modules not replaced.

c22 drafted · lead Bill of materials verification

Check IEC 61215 certification validity and BOM.

c23 drafted · lead Continuous ground fault detection

c24 drafted · lead Material compatibility testing

Select appropriate encapsulant and backsheet materials and test their compatibility.

Referenced by

Data